The overall objective of this proposal is to characterize the retrovirus associated wasting syndrome which occurs in feline leukemia virus infected cats. Like the human immunodeficiency, virus wasting disease, feline wasting syndrome is thought to result from malnutrition associated with gastrointestinal dysfunction. In the proposed study, retrovirus infected cats with either active or latent infection and specific-pathogen-free normal cats will be evaluated for alterations in 1) intestinal and pancreatic structure and kinetics based on histomorphometry and rate of cell replacement, 2) intestinal and pancreatic function based on digestive and absorptive parameters, intestinal barrier maintenance and duodenal microbial quantitation and identifications, and 3) intestinal mucosal lymphoid cell distribution and mitogenic responsiveness compared to systemic and nodal lymphoid cells. Ultimately, an attempt will be made to correlated virologic parameters of infection (i.e. virus exposure, virus expression and replication, viral invasion into intestinal tissue) with changes in gastrointestinal structure and function and mucosal immune responsiveness. The results from the proposed work should provide a better understanding of the role retrovirus infection plays in mediating wasting disease and reveal possible counteractive measures that might be taken to prevent or treat this condition. In addition, the comprehensive characterization of wasting disease in the feline retrovirus/cat disease system will permit, in future studies, its use as an animal model for evaluating experimental therapies.